Is possible is either a bad solenoid or you need to adjust the flap on your automatic sprinkler this is located usually as a small screw you may also have backflow issues or you may want to check the resistance of your cable and make sure power is going to the terminals to the solenoid it may be just enough to turn it on and then stop this indicates usually either a bad wire or not or bad cable

The API in the app should work till DEC 2021 as stated on DarkSkys site. After that, they will have to revert back to one of the other 3 providers.